Conventional radios and other communication devices communicate by generating and receiving a waveform that is fixed through the lifetime of the radio in accordance with one of several communications standards. The various communications standards are not necessarily compatible with one another, leading to situations in which some communication devices are unable to communicate with other such devices. By way of example, many of the cellular telephones used in Europe function according to a communications standard known as the Global System for Mobile Communications (GSM), based on Time Division Multiple Access (TDMA) technology. In contrast, many cellular telephones used in North America function according to communications standards based on Code Division Multiple Access (CDMA) technology. These communications standards are incompatible. Therefore, cellular telephones purchased in North America are often unusable in Europe, and vice versa.
Other exemplary situations arise between the radio equipment of first responder and public safety communities, government agencies, and the military. Frequently, existing communications systems operated by these various agencies do not allow interoperability of the communication equipment. Indeed, it is known that first responders and public safety officers have had great difficulty communicating with each other in emergency situations due to use of such non-interoperable communication equipment. This has led to inefficient communication and miscommunication between the various agencies with grave consequences.
Software defined radios (SDR) have been developed in an attempt to address the problems of incompatible communications standards. An SDR system is a radio communication system which uses software for the modulation and demodulation of radio signals, i.e., waveforms. The hardware of a software-defined radio typically includes a superheterodyne analog radiofrequency (RF) front end that boosts incoming RF signal strength and converts it to a constant frequency, analog to digital and digital to analog converters which are used to convert a digitized signal to and from analog form, and a modem digital signal processor that impresses the digital waveform onto an RF carrier or separates the digital waveform from the RF carrier.
The most significant asset of SDR is versatility. Theoretically, a single SDR set with an all-inclusive software repertoire can be used in any mode, anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite computer program, and making sure the batteries are adequately charged if portable operation is contemplated. Consequently, software defined radios have significant utility for the military and cellular telephone services, both of which must serve a wide variety of evolving radio communications standards in real time. However, a single SDR could ultimately be capable of playing the roles of cordless telephone, cellular telephone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System unit, and other evolving functions.
Many software defined radios are built from a large number of chips in order to provide an adequate range of flexible resources to anticipate all the requirements of the variety of communications standards. This large number of chips leads to an SDR that is both bulky and expensive to manufacture.
Other prior art software defined radios include a general purpose processor (GPP), a digital signal processor (DSP), and a field programmable gate array (FPGA) as a modem resource. The FPGA is programmed to perform the high speed signal processes which are too fast to be performed in the DSP or the GPP. The FPGA also includes the glue logic (simple logic circuits used to connect complex logic circuits together) and performs timing of time slotted communications standards.
This SDR configuration reduces the number of chips relative to prior art SDRs, thereby reducing bulk. Unfortunately, FPGAs are very expensive and generally slower than their application-specific integrated circuit (ASIC) counterparts and draw more power. In addition, FPGAs generate undesirably high direct current (DC) leakage current, which is used to remember the circuit topology of the FPGA. Thus, battery lifetime for many applications may be inadequate.
Accordingly, what is needed is a modem resource for communications devices, such as a software defined radio, that is capable of processing multiple waveforms inexpensively and efficiently.